power: supply: axp288: use the BIT() macro

Make use of the recommended BIT() macro for bit defines.

Signed-off-by: Olliver Schinagl <oliver@schinagl.nl>
Signed-off-by: Priit Laes <plaes@plaes.org>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>